1. Field of the Invention
This invention is related to extrusion process apparatus and more particularly, to associated devices for the prevention of and/or assisting the removal of a jammed extrudate from a cooling chamber associated with the extrusion process apparatus.
2. State of the Prior Art
It is known to form certain types of continuous stock workpieces, such as rod and tubular shaped articles, from thermoplastic material by extruding the same as a heated extrudate from an extruder followed by passage of the heated extrudate through a cooling bath to remove heat therefrom to set or rigidize the material of the continuous stock which thereafter may be sectioned into individual articles for a particular intended end use. The extrudate further may be shaped and sized by passing the same through a closing or sizing aperture located advantageously at the entrance to the cooling bath. U.S. Pat. Nos. 3,538,210 and 3,579,623 both describe methods with which tubular articles can be made, such articles being characterized by having circumferential dimension of precise nature within a particular range of values. As is well-known in the extrusion art, and as is exemplified by the aforementioned patents, the extrudate if it is in tubular form generally will be issued from the extruder at a size somewhat larger than the final finished product and then directed through the sizing aperture to draw down the extrudate to the requisite final dimension. The extrudate will have, for formation of a workpiece of given size and with respect to the extrudate line speed and placement of extruder in relation to the cooling bath entrance, a predetermined dimension during its travel from the extruder to the sizing aperture, such predetermined dimension diminishing uniformally as the extrudate approaches the closing aperture. If for any reason the extrudate should leave the extruding means at an outsized dimension, that is at a dimension greater than intended either by way of overall workpiece diameter at any given location, or by reason of greater thickness of the tube wall than intended, it is possible for the outsized extrudate upon entry through the closing aperture to jam the same. This can result in shutdown of the forming line apparatus as well as requiring that the aperture be freed, a not easy task because the plastic state extrudate when solidified in the aperture is difficult and time consuming to remove. Furthermore, if the extrudate were outsized to a point that it would cause a jam in the sizing aperture and a breakage in the extrudate occurred without fully jamming the sizing aperture, it is probable that cooling liquid from the bath thereof would escape through the aperture and splash onto adjacent machinery including the extruding apparatus to the detriment of the latter.
In the above mentioned U.S. Pat. No. 3,538,210, there is shown extrusion apparatus including a liquid filled cooling chamber having an entry therein through a sizing aperture which has a tendency to be jammed by an outsized extrudate. Within the cooling chamber, there is disposed an assembly of sizing discs longitudinally spaced of each other to successively size the extrudate that is being drawn through the cooling chamber. The assembly of sizing plates is secured together in the noted patent by a plurality of elongated threaded connecting rods, the rods being enclosed by spacer sleeves to space the successively aligned sizing discs. Further, there is disclosed that lateral support for the foredescribed assembly is provided by a plurality of side braces interconnected between a side of the cooling chamber and the elongated connecting rods. In the event that the extrudate that is being drawn through the cooling chamber should jam, it will often be necessary to remove the sizing disc assembly from the cooling chamber, to be disassembled whereby the extrudate may be cleaned and removed from the sizing discs. It is understood that such a process is time consuming resulting often in the prolonged shut down of the extrusion process apparatus.
In U.S. Pat. No. 3,813,200 there is disclosed a device for preventing a jam of the sizing aperture into a cooling chamber through which the extrudate is drawn. In particular, the jam preventing device includes an electrical optical assembly for detecting an outsized extrudate, in the form of a light beam projecting element and a photosensitive element disposed to receive normally the light beam that is directed in the vicinity of the entrance sizing aperture. Upon detection of the outsized extrudate, a cutter blade is actuated to move from a first to a second position across the entrance sizing aperture, whereby the extrudate is severed at that point permitting it to be drawn through the cooling chamber. At the same time, the extruder is deactuated whereby no more extrudate is introduced into the cooling chamber. In the above-identified co-pending application of Gergely, there is disclosed an improvement of this jamming device, wherein a circular blade is rotated to provide a relatively fast cutting motion to sever the extrudate at the entrance sizing aperture.